Centrifugal separator with pumping means, arranged to accomplish a circulating flow

ABSTRACT

In a centrifugal separator there is formed within the rotor a separating chamber (7) and a central chamber (26), which latter communicates with a peripheral part of the separating chamber through a channel (19a, 19b). The part (19a) of the channel situated closest to the central chamber (26) extends substantially parallel with the rotor axis, whereas the other channel part (19b) forms an angle with the rotor axis. For avoiding that solids entrained by liquid entering the channel (19a, 19b) from the separating chamber (7) are separated and depositing on the outer wall of the inner channel part (19a) a partition member (44) is arranged in this inner channel part (19a). The partition member (44) divides the channel part (19a) into two parallel flow ways (45, 46). Further, a pumping means (31) is arranged to pump liquid from the central chamber (26) to one (45) of said flow ways, so that this liquid flows through first said one (45) and then said other (46) flow way and then flows back to the central chamber (26). By the liquid circulation thus established in the inner channel part (19a) the solids are maintained suspended in the liquid until it again leaves the channel part (19a).

The present invention relates to a centrifugal separator for separationof solids from a suspension, comprising a rotor that forms a separatingchamber having a central part and a peripheral part, means definingwithin the rotor a central chamber and a channel, which latter connectsthe central chamber with said peripheral part of the separating chamber,a first part of the channel close to the central chamber extendingsubstantially parallel with the rotor axis, and a second part of thechannel forming an angle with the rotor axis and extending from saidfirst channel part to the peripheral part of the separating chamber.

A centrifugal separator of this kind is disclosed for instance in U.S.Pat. Nos. 3,752,389 and 4,525,155.

A problem in connection with operation of a centrifugal separator ofthis kind is that solid particles in the treated suspension areentrained by liquid into said channel and are depositing on the radiallyouter wall of said first part of the channel extending substantially inparallel with the rotor axis. In certain cases it has proved that suchdepositing of particles has entirely, or to a substantial degree,blocked liquid flow through the channel and, thereby, jeopardized theintended function of the centrifugal separator.

As can be seen from said patent specification the channel in question ina centrifugal separator of this kind may have different functions. Inthe centrifugal separator according to U.S. Pat. No. 4,525,155 thechannel is intended to be flowed through intermittently by a relativelyheavy liquid that has been separated in the rotor and is to bedischarged therefrom. In the centrifugal separator according to U.S.Pat. No. 3,752,389 the corresponding channel is both to be flowedthrough intermittently by separated heavy liquid to be discharged fromthe rotor and, substantially continuously, to be flowed through by asmall flow of liquid intended for sensing purpose. In both these casesparticles will be entrained by liquid from the separating chamber intothe channel and deposit on the radially outer wall of said first part ofthe channel. Since this outer wall has only an insignificantinclination, or no inclination at all, relative to the rotor axis,particle deposits thereon cannot move along the outer wall as aconsequence of the centrifugal force. Therefore, they remain and causeclogging of the channel.

A different function of said channel may be to transfer liquidintermittently from a stationary member to the radially outermost partof the separating chamber. Such liquid may be a so called displacementliquid that is supplied to the separating chamber in a certain amountimmediately before a brief opening of the peripheral outlets of theseparating chamber. It has proved in practice that clogging problemshave arisen even in these cases--probably as a consequence of particleshaving been entrained by liquid from the separating chamber into saidchannel after each time the peripheral outlets of the separating chamberhave been opened. The particles then have deposited on said outer wallin the first part of the channel, where they have remained even duringthe repeated periods of time when the channel has been emptied ofliquid. New particles then have been entrained by liquid from theseparating chamber into the channel, etc.

The object of the present invention is to avoid collection of particlesin said first part of the channel in a centrifugal separator of theinitially described kind.

This object may be obtained in that the centrifugal separator comprisesa pumping means, for instance of the kind shown in U.S. Pat. No.4,525,155, which is arranged during operation of the rotor to pumpliquid out of the central chamber and thereby to establish a liquid flowthrough the initially mentioned channel and into the central chamber,and that this pumping means is arranged to pump liquid from the centralchamber to an area in said channel so situated that a circulation of thepumped liquid will come up in a flow circuit comprising said first partof the channel, the central chamber and the pumping means.

Preferably, the pumping means is arranged to pump liquid from thecentral chamber to the area of the channel, where said parts of thechannels communicate with each other. However, pumping of liquid fromthe central chamber to any area within said second part of the channelwill create a circulation flow of liquid through said first part of thechannel without by itself causing solids to pass from the separatingchamber into the channel.

By this invention a so strong liquid flow can constantly be maintainedin said first part of the channel that particles present in the liquidare prevented from separating from the liquid and depositing on theouter wall of said channel part. Particles entrained by liquid into saidchannel part will thus accompany the liquid even out of it.

This means in a case such as the one according to U.S. Pat. No.3,752,389, where a small flow of liquid is to be maintained continuouslyfrom the radially outer part of the separating chamber and out of therotor through said channel, that a substantially stronger flow of liquidmay be obtained at least in said first channel part, in which theradially outer wall extends substantially parallel with the rotor axis.

In a case where the channel is intended only for a liquid flow from thecentral chamber to the separating chamber, the invention means thatparticles which cannot be prevented from accompanying the liquid fromthe separating chamber into the channel can be maintained suspended inthe liquid until it flows back to the separating chamber in connectionwith opening of its peripheral outlets for separated solids.

A preferred embodiment of the invention is characterized in that therotor has a partition member, which is formed and arranged such in saidfirst part of the channel that this channel part is divided into atleast two parallel flow ways; that only one of the flow ways isconnected to the central chamber, and that the pumping means is arrangedto pump liquid from the central chamber to the other flow way, so thatliquid will flow in a direction away from the central chamber along saidother flow way and in a direction towards the central chamber along saidone flow way. Hereby, the pumping means may be given a short axialextension in that the inlet and outlet of the pumping means may besituated axially very close to each other.

Said partition member, within the scope of the invention, may dividesaid first channel part into several flow ways which are situated at thesame distance from the rotor axis and are evenly distributedtherearound. For instance, every second one of the flow ways may beconnected to the central chamber in order to be flowed through by liquidin one direction, whereas the rest of the flow ways are arranged toreceive liquid from the pumping means in order to be flowed through byliquid in the opposite direction.

Preferably, however, the partition member divides the first channel partin a radially inner and a radially outer flow way, which flow waysextend substantially annularly around the rotor axis.

The invention is described in the following with reference to theaccompanying drawing.

FIG. 1 shows part of a previously known centrifugal separator, seen inan axial section.

FIG. 2 shows a part of the centrifugal separator according to FIG. 1,which has been modified in accordance with the invention.

The previously known centrifugal separator in FIG. 1 comprises a rotorconsisting of two parts 1 and 2, which are kept together by means of alocking ring 3. The rotor is supported by a drive shaft 4.

Within the rotor a slide 5 is axially movable to and from sealingagainst an annular gasket 6. Between the slide 5 and the upper rotorpart 1 a separating chamber 7 is defined, and between the slide 5 andthe lower rotor part 2 a chamber 8 is defined and intended to contain socalled operating liquid.

Means 9 are arranged for supply of operating liquid to a space 10defined in the rotor part 2, from which space a channel 11 leads to thesaid chamber 8. A throttled channel 12 leads from the radially outermostpart of the chamber 8 through the rotor part 2 to the outside of therotor.

In the separating chamber 7 a set of conical separating discs 13 isarranged. These rest on a so called distributor 14, which in the lowerpart of the rotor forms together with a conical disc 15 an inlet 16 tothe separating chamber 7.

The upper part of the distributor 14 surrounds a central space in therotor, into which a stationary pipe 17 extends for the supply of amixture of components to be separated in the rotor.

On the top of the set of discs in the separating chamber (only a fewdiscs 13 are shown in the drawing) there is resting a conical top disc18, which is thicker than the discs 13 and extends somewhat longerradially outwards than these in the separating chamber. The disc 18forms together with the upper rotor part 1 a channel consisting of twochannel parts 19a and 19b, and has at about the radial level of theouter edges of the separating discs a through-hole 20. The channel part19a extends substantially parallel with the rotor axis, whereas thechannel part 19b forms an angle with the rotor axis.

In the upper part of the rotor the top disc 18 has two radially inwardsdirected annular flanges 21 and 22, which between themselves form achamber 23. The upper flange 22 extends longer radially inwards than theflange 21. Above the uppermost flange 22 the upper rotor part 1 has aninwardly directed annular flange 24, which extends radially inwardssomewhat longer than the lowermost flange 21. Between the flanges 24 and22 there is left a space 25 communicating through the channel 19a, 19bwith the separating chamber 7.

Between the uppermost portion of the rotor part 1 and the flange 24supported thereby there is formed a chamber 26 which communicates withsaid space 25 through a calibrated opening 27 in the flange 24.

The previously described inlet pipe 17 supports a pipe 28, whichcoaxially surrounds the inlet pipe and at its lower end supports a socalled paring disc 29. The paring disc 29 is arranged in thebefore-mentioned chamber 23.

In its turn the pipe 28 supports a surrounding pipe 30, which at itslower end supports a paring disc 31. The paring disc 31 is arrangedwithin the before-mentioned chamber 26 and has several channels32--distributed around the paring disc--which through an annular channel33 communicate with an outlet conduit 34. In the outlet conduit 34 thereis arranged a closing valve 35.

In one or some of its channels 32 the paring disc 31 has a calibratedopening 36, which thus constitutes a calibrated outlet from theconnection extending between the chamber 26 and the valve 35.

The previously mentioned paring disc 29 has paring channels 37, whichthrough an annular channel 38 communicate with a conduit 39. In theconduit 39 sensing means 40 of some conventional kind is arranged tosense if a certain liquid flowing through the conduit 39 containsfractions of another liquid.

A control equipment 41 is connected via connections 42 and 43 to thesensing means 40 and the valve 35, respectively.

The above described centrifugal separator may be used for cleaning ofoil, for instance heavy fuel oil, from water and solid particles. Amixture of these components, heated to about 100° C., is to be suppliedto the centrifuge rotor through the conduit 17, from where it will flowthrough the channel 16 into the separating chamber 7.

At this stage the chamber 8 between the slide 5 and the rotor part 2 isfilled with operating water, so that the slide 5 is kept pressed againstthe gasket 6. A small amount of operating water constantly leaves thechamber 8 through the hole 12, but a corresponding amount of newoperating water is continuously supplied through the means 9.

In the separating chamber 7 separated oil moves towards the rotor centreand flows into the chamber 23, from which it is pumped by the paringdisc 29 through the channels 37 and 38 to the outlet conduit 39. Theradially inwards directed annular flange 21 forms an overflow outletfrom the separating chamber for the separated oil, so that the liquidlevel in the separating chamber is determined by the position of theinner edge of the flange 21.

Separated oil will flow towards the rotor centre also in the channel19a, 19b between the top disc 18 and the rotor part 1. From the channelpart 19a the oil enters the central space 25, where a free liquidsurface is formed at the same level as in the separating chamber 7.

A certain amount of oil flows through the calibrated opening 27 in theflange 24 into the chamber 26. From there oil is pumped by the paringdisc 31 through the channels 32 and 33 out into the conduit 34 to thevalve 35. In a starting position the valve 35 is closed and, therefore,no further oil flow through the conduit 34 will take place after thechannels 32 and 33 and the conduit 34 have been filled. The paring disc31 will continue, however, to pump oil out of the chamber 26, which oilleaves through the calibrated outlet 36 some distance within one of theparing disc channels 32. The oil flowing out through the outlet 36 willenter the space 25, where it cannot influence on the liquid level andfrom where it may again flow into the chamber 26 through the opening 27.

By the constant pumping of oil out of the chamber 26 the free liquidsurface therein may be kept at a level radially outside of the freeliquid surface in the space 25 while the valve 35 in the conduit 34 isclosed.

When after some time of operation so much separated water has beencollected in the radially outer part of the separating chamber that theinterface layer between oil and water is situated at a level A in theseparating chamber, fractions of water start to be entrained by theseparated oil leaving through the conduit 39. This is sensed by themeans 40, which emit a signal to the control equipment 41. In turn thecontrol equipment 41 causes the valve 35 to open and to be kept openduring a predetermined period of time. During this period of time somuch separated water leaves the separating chamber 7 through the channel19a, 19b, passing through the flow determining opening 27 in the flange24, that the interface layer in the separating chamber between oil andwater moves to a level B.

After the valve 35 has been closed, the water which in this stage ispresent within the chamber 26, the space 27 and the channel 19a, 19bwill flow back to the separating chamber, oil then flowing through thehole 20 in the top disc 18 and refilling said spaces to the levels shownin the drawing.

In the way described above separated water may be intermittentlyconducted away from the separating chamber 7. Solid particles havingbeen separated in the separating chamber as a rule have to be dischargedmore seldomly. This can be accomplished by occasionally interrupting thesupply of operating water through the supply means 9. The controlequipment 41 then may be so programmed, that for instance every fourthtime a signal is emitted thereto, indicating that the interface layerbetween oil and water in the separating chamber has reached the level A,the valve 35 is maintained closed, whereas instead the supply ofoperating liquid to the means 9 is occasionally interrupted. In this waythe slide 5 is caused to move axially downwards leaving an open slotbetween itself and the gasket 6. Separated solids and a desired amountof water then leave the separating chamber 7 through this slot andthrough ports situated radially outside of the slot in the rotor part 2.

FIG. 2 shows a part of the centrifugal separator according to FIG. 1,which has been provided with an annular partition member 44. Acylindrical part of the partition member 44 divides the channel part 19a(FIG. 1) in a radially inner flow way 45 (FIG. 2) and a radially outerflow way 46 (FIG. 2), whereas a plane part of the partition member 44divides the space 25 (FIG. 1) into a lower compartment 25a (FIG. 2)communicating with said inner flow way 45, and an upper compartment 25b(FIG. 2) communicating with said outer flow way 46.

The partition member 44 also has a radially inner part in the form of ashort cylinder extending axially past and radially inside of the flange24. This part of the partition member is situated at a distance from therotor axis which is larger than that for each opening 36 in the paringdisc 31. Thereby it is assured that liquid flowing out of the paringdisc 31 through the opening 36 is supplied to the lower compartment 25a.

During operation of the centrifugal separator according to FIG. 2 liquidwill thus always be pumped by means of the paring disc 31 from thechamber 26 through the opening 36 to the compartment 25a. Hence, theliquid flows further on through the flow way 45 to the lowermost end ofthe partition member 44, where it turns around and flows in the oppositedirection through the flow way 46 and the calibrated opening 27 back tothe chamber 26. A liquid flow of this kind will be maintained even whenthe valve 35 in the conduit 34 (FIG. 1) is closed, whereby is preventedthat solids having been entrained by the liquid from the separatingchamber 7 through the channel part 19b to the channel part 19a (FIG. 1)are separated and deposit in the channel 19a. Accompanying particles ofthis kind will instead remain suspended in the liquid being circulatedby means of the paring disc 31 in the flow circuit 26, 32, 36, 25a, 45,46 and 27, and they will accompany the liquid sooner or later when itleaves the flow circuit. This occurs either through the conduit 34, whenthe valve 35 is opened, or through the channel part 19b, when the slide5 is moved axially for discharge of separated sludge from the separatingchamber 7.

It is possible that part of the particles, which are being entrained bythe circulating liquid while the valve 35 is closed, are separated atthe lowermost end of the partition member 44 and are returned by thecentrifugal force to the separating chamber 7 through the channel part19b.

The invention has been described above in connection with a centrifugalseparator in which the paring disc 31 is arranged to pump a separatedrelatively heavy liquid out of the rotor. The invention advantageouslymay be used also in connection with a centrifugal separator, the rotorof which has only two outlets, i.e. a central outlet intended for aseparated relatively light liquid and a peripheral outlet intended forboth separated solids and a separated relatively heavy liquid.

I claim:
 1. A centrifugal separator for the separation of solids from aliquid suspension, comprising a rotor, the rotor forming a separatingchamber having a central part and a peripheral part, means definingwithin the rotor a central chamber and a channel, the channel having twoends, one said end communicating with the central chamber and theopposite end communicating with the peripheral part of the separatingchamber, a first part of the channel being positioned close to thecentral chamber and extending substantially parallel with the rotoraxis, a second part of the channel forming an angle with the rotor axisand extending from the first channel part to the peripheral part of theseparating chamber, and pumping means arranged during operation of therotor to pump liquid out of the central chamber and, thereby, toaccomplish a liquid flow through said channel and into the centralchamber, wherein the pumping means is arranged to pump liquid from thecentral chamber to an area of said channel spaced from said opposite endthereof communicating with the separation chamber such that arecirculation flow of the pumped liquid will be established spaced fromthis opposite end of the channel, the recirculation flow forming a flowcircuit comprising said first part of the channel, the central chamberand the pumping means.
 2. A centrifugal separator according to claim 1,wherein the pumping means is arranged to pump liquid from the centralchamber to an area of said channel, where said channel parts communicatewith each other.
 3. A centrifugal separator for separation of solidsfrom a liquid suspension, comprising a rotor, the rotor forming aseparating chamber having a central part and a peripheral part, meansdefining within the rotor a central chamber and a channel, the channelconnecting the central chamber with the peripheral part of theseparating chamber, a first part of the channel close to the centralchamber extending substantially parallel with the rotor axis and asecond part of the channel forming an angle with the rotor axis andextending from the first channel part to the peripheral part of theseparating chamber, and pumping means arranged during operation of therotor to pump liquid out of the central chamber and, thereby, toaccomplish a liquid flow through said channel and into the centralchamber, wherein the pumping means is arranged to pump liquid from thecentral chamber to an area of said channel so situated that acirculation flow of the pumped liquid will be established and forming aflow circuit comprising said first part of the channel, the centralchamber and the pumping means, the rotor having a partition member, thepartition member being formed and arranged such that said first part ofthe channel is divided into at least two parallel flow ways, only one ofsaid flow ways being connected to the central chamber, and the pumpingmeans being arranged to pump liquid from the central chamber to theother flow way, so that liquid flows in a direction from the centralchamber along said other flow way and in a direction towards the centralchamber along said one flow way.
 4. A centrifugal separator according toclaim 3, wherein the partition member divides the first channel part ina radially inner flow way and a radially outer flow way.
 5. Acentrifugal separator according to claim 4, wherein the partition memberis substantially annular.
 6. A centrifugal separator according to claim3, wherein means is arranged to maintain during operation of the rotor afree liquid surface at a predetermined radial level in a space formed inthe rotor and communicating through said first and second parts of thechannel with the separating chamber, a further partition in the rotorseparates the central chamber from said one flow way in the firstchannel part and has at least one calibrated through-hole, the partitionmember and further partition define a radially inward open space in therotor, which communicates with said one flow way in the first channelpart and the partition member extends radially inward in the rotor to alevel inside said predetermined radial level.
 7. A centrifugal separatorfor separation of solids from a liquid suspension, comprising a rotor,the rotor forming a separating chamber having a central part and aperipheral part, means defining within the rotor a central chamber and achannel, the channel connecting the central chamber with the peripheralpart of the separating chamber, a first part of the channel close to thecentral chamber extending substantially parallel with the rotor axis anda second part of the channel forming an angle with the rotor axis andextending from the first channel part to the peripheral part of theseparating chamber, and pumping means arranged during operation of therotor to pump liquid out of the central chamber and, thereby, toaccomplish a liquid flow through said channel and into the centralchamber, wherein the pumping means is arranged to pump liquid from thecentral chamber to an area of said channel so situated that acirculation flow of the pumped liquid will be established and forming aflow circuit comprising said first part of the channel, the centralchamber and the pumping means, the pumping means being arranged to pumpliquid from the central chamber to an area of said channel, where saidchannel parts communicate with each other, the rotor having a partitionmember formed and arranged such that said first part of the channel isdivided into at least two parallel flow ways, one of said flow waysbeing connected to the central chamber, and the pumping means beingarranged to pump liquid from the central chamber to the other flow wayso that liquid flows in a direction from the central chamber along saidother flow way and in a direction towards the central chamber along saidone flow way.
 8. A centrifugal separator according to claim 7, whereinthe partition member divides the first channel part in a radially innerflow way and a radially outer flow way.
 9. A centrifugal separatoraccording to claim 8, wherein the partition member is substantiallyannular.
 10. A centrifugal separator according to claim 9, wherein meansis arranged to maintain during operation of the rotor a free liquidsurface at a predetermined radial level in a space formed in the rotorand communicating through said first and second parts of the channelwith a separating chamber, a further partition in the rotor separatesthe central chamber from said one flow way in the first channel part andhas at least one calibrated through-hole, the partition member andfurther partition define a radially inward open space in the rotor whichcommunicates with said one flow way in the first channel part, and thepartition member extends radially inward in the rotor to a level insidesaid predetermined radial level.
 11. A centrifugal separator forseparation of solids from a liquid suspension, comprising a rotor, therotor forming a separating chamber having a central part and aperipheral part, means defining within the rotor a central chamber and achannel, the channel having two ends and connecting the central chamberthrough one of its ends with the peripheral part of the separatingchamber through its other end, a first part of the channel close to thecentral chamber extending substantially parallel with the rotor axis anda second part of the channel forming an angle with the rotor axis andextending from the first channel part to the peripheral part of theseparating chamber, and pumping means arranged during operation of therotor to pump liquid out of the central chamber and, thereby, toaccomplish a liquid flow through said channel and into the centralchamber, wherein the pumping means is arranged to pump liquid from thecentral chamber to an area of said channel so situated that acirculation flow of the pumped liquid will be established spaced fromsaid other end of the channel and forming a flow circuit comprising saidfirst part of the channel, the central chamber and the pumping means,the rotor having a partition member, the partition member being formedand arranged such that said first part of the channel is divided into atleast two parallel flow ways, only one of said flow ways being connectedto the central chamber, and the pumping means being arranged to pumpliquid from the central chamber to the other flow way, so that liquidflows in a direction from the central chamber along said other flow wayand in a direction towards the central chamber along said one flow way.12. A centrifugal separator for separation of solids from a liquidsuspension, comprising a rotor, the rotor forming a separating chamberhaving a central part and a peripheral part, means defining within therotor a central chamber and a channel, the channel having two ends andconnecting the central chamber through one of its ends with theperipheral part of the separating chamber through its other end, a firstpart of the channel close to the central chamber extending substantiallyparallel with the rotor axis and a second part of the channel forming anangle with the rotor axis and extending from the first channel part tothe peripheral part of the separating chamber, and pumping meansarranged during operation of the rotor to pump liquid out of the centralchamber and, thereby, to accomplish a liquid flow through said channeland into the central chamber, wherein the pumping means is arranged topump liquid from the central chamber to an area of said channel sosituated that a circulation flow of the pumped liquid will beestablished spaced from said other end of the channel and forming a flowcircuit comprising said first part of the channel, the central chamberand the pumping means, the pumping means being arranged to pump liquidfrom the central chamber to an area of said channel, where said channelparts communicate with each other, the rotor having a partition memberformed and arranged such that said first part of the channel is dividedinto at least two parallel flow ways, one of said flow ways beingconnected to the central chamber, and the pumping means being arrangedto pump liquid from the central chamber to the other flow way so thatliquid flows in a direction from the central chamber along said otherflow way and in a direction towards the central chamber along said oneflow way.